Resonance Irradiation of Mercury Vapor in Nitrogen

Abstract

A study has been made of phenomena related to the metastable $6^{3}P_{0}$ mercury atom appearing in a cell which contains nitrogen and saturated mercury vapor at 22\ifmmode^\circ\else\textdegree\fi{}C and is irradiated with 2537 A ($6^{1}S_{0}\ensuremath{-}6^{3}P_{1}$) resonance emission from a cool mercury arc. Various phenomena reported individually by many investigators are observed simultaneously and with improved techniques so that coherent correlations can be drawn and new conclusions developed. The relative $6^{3}P_{0}$ population produced from $6^{3}P_{1}$ atoms by inelastic collision is measured by self-absorption of 4047 A ($6^{3}P_{0}\ensuremath{-}7^{3}S_{1}$); its dependence upon 2537 A intensity is linear and its dependence upon nitrogen pressure is given by theory. The $6^{3}P_{1}$ population is quenched by nitrogen. With conditions of high gas purity it is possible to produce large currents of heavy ions, the probable mechanism being a three-body collision between $6^{3}P_{0}$, $6^{3}P_{1}$, and ${\mathrm{N}}_{2}$ to form a highly excited molecule, which becomes ionized in a subsequent step. The ion formation is a volume process, varying with the second power of the 2537 A intensity. The continuum intensity near 4850 A is linear with 2537 A intensity and shows a pressure dependence consistent with molecular formation in a three-body collision between $6^{3}P_{0}$, $6^{1}S_{0}$, and ${\mathrm{N}}_{2}$. Mean lifetimes of metastable population, ion formation, and continuum intensity are measured as a function of pressure of nitrogen. They are found to differ distinctly, being generally larger in the order named. At high irradiation intensity an ion current of 405 \ensuremath{\mu}a was observed, leading to a prediction that several percent of the mercury atoms could be in the metastable state.